1. Field of the Invention
The present invention relates generally to disk drives and more particularly to a method, apparatus, and computer readable program code for improving performance and robustness of hard disk drive servomechanisms.
2. Description of the Related Art
Hard disk drives include a plurality of magnetic transducers that can write and read information by magnetizing and sensing the magnetic field of a rotating disk(s), respectively. The information is typically formatted into a plurality of sectors that are located within an annular track. There are a number of tracks located across each surface of the disk. A number of vertically similar tracks are sometimes referred to as a cylinder. Each track may therefore be identified by a cylinder number.
Each transducer is typically integrated into a slider that is incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm. The actuator arm has a voice coil located adjacent to a magnet assembly which together define a voice coil motor. The hard disk drive typically includes a driver circuit and a controller that provide current to excite the voice coil motor. The excited voice coil motor rotates the actuator arm and moves the transducers across the surfaces of the disk(s).
When writing or reading information the hard disk drive may perform a seek routine to move the transducers from one cylinder (track) to another cylinder. During the seek routine the voice coil motor is excited with a current to move the transducers to the new cylinder location on the disk surfaces. The controller also performs a servo routine to insure that the transducer is at the center of the track.
Many disk drives utilize a xe2x80x9cbang-bangxe2x80x9d control algorithm to move the transducer to the correct location in the shortest amount of time. The shape of the current waveform for seek routines that utilize bang-bang control theory is typically square. Unfortunately, square waveforms contain high frequency harmonics which stimulate mechanical resonance in the HGA and excite mechanical components or assemblies with high natural frequencies. This results in acoustic noise, and undesirable vibration and associated settling time due to residual vibration. The mechanical resonance created by the square waveforms of the prior art tend to increase both the settling and overall time required to write or read information from the disk.
It is desirable to minimize the amount of time required to write and read information from the disk(s). Therefore, the seek routine performed by the drive should move the transducers to the new cylinder location in the shortest amount of time. Additionally, the settling time of the HGA should be minimized so that the transducer can quickly write or read information, once located adjacent to the new cylinder.
Another seek technique is described in a co-pending application entitled xe2x80x9cMETHOD AND APPARATUS FOR REDUCING ACOUSTIC NOISE IN A HARD DISK DRIVExe2x80x9d, application Ser. No. 09/167,884, filed Oct. 7, 1998, and assigned to the assignee of the present invention. The co-pending application describes a sinusoidal seek method that reduces acoustic noise in seeking.
The present invention comprises a method, apparatus, and computer program product for a hard disk drive servomechanism. In one embodiment, the apparatus comprises a disk which has a surface, a spindle motor that rotates the disk, a transducer which can write information onto the disk and read information from the disk, and an actuator arm that can move the transducer across the surface of the disk. The apparatus further includes a controller that controls the actuator arm to move the transducer across the disk surface using a generalized Fourier series seek acceleration trajectory having one or more tuned coefficients.